Use an alternate stack for signal handling #1847
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stevenengler
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Cool! I verified that #1549 works for me now with the latest go version.
Partially addresses shadow#1549
This prevents managed calls to sigaltstack from interfering with the shim's own configured sigaltstack. The current fakery should be good enough until if and when a managed program's signal handler is invoked. preload mode is already broken in that case, though. Once signal handlers in preload mode are working, we probably ought to emulate this more faithfuly, since it may be difficult to debug if the program goes wrong because *our* altstack wasn't big enough, or it somehow detected it wasn't running on the configured stack etc.
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Configure the shim's signal handlers (which are only used in preload mode) to use an alternate stack via
sigaltstack. Experimentally this appears to fix the stack corruption observed in #1549.In preload mode, also prevent managed calls to
sigaltstackfrom overwriting our configuration. Eventually this should be implemented more faithfully, but this should be good enough at least until we're to the point of being able to invoke signal handlers configured by the managed process.This is "milestone 1" of #1851